Method for recognizing license plate in vehicle camera device and vehicle camera device

ABSTRACT

A vehicle camera device is applied in a vehicle. The vehicle camera device performs image recognition of current driving image to obtain a license-plate pattern in the driving image, and when size of the license-plate pattern is less than a threshold, increases a focus according to current speed of the vehicle.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority of China Patent Application No.201710950150.2 filed on Oct. 13, 2017, the entirety of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to event data recorders and, moreparticularly, to a method for recognizing a license plate with a vehiclecamera device and the vehicle camera device.

Description of the Prior Art

Vehicles are regarded as a means of transport indispensable to everysociety nowadays. Vehicles are on the rise, so are traffic accidentdisputes. Safe driving on diverse, unpredictable roads necessitatesdifferent safety devices mounted on vehicles. The safety devices fallwithin two categories: active auxiliary driving devices and vehiclecamera devices. The former detects distances between vehicles andgenerates an alert which warns drivers of overly short distances. Thelatter, for example, an event data recorder, passively records howvehicles are moving.

In case of a traffic accident dispute, liability investigation will bebased on images captured by roadside picture-taking devices, imagescaptured by an event data recorder mounted on every vehicle involved inthe accident, and/or images captured by an event data recorder mountedon every vehicle passing the scene of the traffic accident at the pointin time when the traffic accident happens. To identify the vehicle(s)held accountable for the traffic accident, some event data recorders areeven capable of license plate recognition. However, images captured bythe event data recorders are unclear because of the motion of thevehicles; hence, genuineness of license plate numbers thus recognized isin doubt.

SUMMARY OF THE INVENTION

In an embodiment, a method for recognizing a license plate with avehicle camera device is provided and adapted for use with a vehicle.The method comprises the steps of: capturing a first driving image by apicture-taking module with a focal length of a first assigned value;performing image recognition on the first driving image to search thefirst driving image for a license-plate picture; detecting a picturesize of the license-plate picture according to a size threshold;increasing the focal length from the first assigned value to a secondassigned value according to a speed of the vehicle when the picture sizeof the license-plate picture is smaller than the size threshold; andcapturing a second driving image by the picture-taking module with thefocal length of the second assigned value.

In another embodiment, a vehicle camera device is provided and adaptedto be disposed on a vehicle. The vehicle camera device comprises apicture-taking module, an image analyzing unit, an adjusting unit and adetermining unit. The picture-taking module captures a driving imagewith a focal length. The image analyzing unit performs image recognitionon the driving image to search the driving image for a license-platepicture. The adjusting unit receives a speed of the vehicle. Thedetermining unit detects a picture size of the license-plate pictureaccording to a size threshold and causes the adjusting unit to increasethe focal length of the picture-taking module according to the speed ofthe vehicle when the picture size of the license-plate picture issmaller than the size threshold.

In yet another embodiment, a method for recognizing a license plate witha vehicle camera device comprises: assigning an input value which is afunction of the speed of the vehicle to a focal length of thepicture-taking module, capturing a driving image by the picture-takingmodule with the focal length assigned, searching the driving image for alicense-plate picture, and recognizing the license-plate picture found.

In conclusion, a method for recognizing a license plate with a vehiclecamera device and the vehicle camera device according to the presentinvention are adapted for use with a vehicle. The focal length of thevehicle camera device is adjusted in response to the speed of thevehicle to increase the recognition rate of a license-plate picturefound in a driving image captured with the vehicle camera device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a vehicle camera device according to anembodiment of the present invention;

FIG. 2 is a schematic view of implementation of the vehicle cameradevice of FIG. 1;

FIG. 3 is a flowchart of a method for recognizing a license plate with avehicle camera device according to the first embodiment of the presentinvention;

FIG. 4 is a partial flowchart of a method for recognizing a licenseplate with a vehicle camera device according to the second embodiment ofthe present invention;

FIG. 5 is a partial flowchart of a method for recognizing a licenseplate with a vehicle camera device according to the third embodiment ofthe present invention;

FIG. 6 is a partial flowchart of a method for recognizing a licenseplate with a vehicle camera device according to the fourth embodiment ofthe present invention;

FIG. 7 is a flowchart of a method for recognizing a license plate with avehicle camera device according to the fifth embodiment of the presentinvention; and

FIG. 8 is a partial flowchart of a method for recognizing a licenseplate with a vehicle camera device according to the sixth embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a block diagram of a vehicle camera device according to anembodiment of the present invention. FIG. 2 is a schematic view ofimplementation of the vehicle camera device of FIG. 1.

Referring to FIG. 1 and FIG. 2, a vehicle camera device 10 is adapted tobe disposed on a vehicle 20. In some embodiments, the vehicle cameradevice 10 is mounted on the vehicle 20 and faces in the direction inwhich the vehicle 20 moves forward to take pictures.

The vehicle camera device 10 comprises a picture-taking module 110, animage analyzing unit 120, an adjusting unit 130 and a determining unit140. The image analyzing unit 120 is connected between thepicture-taking module 110 and the determining unit 140. The adjustingunit 130 is connected between the picture-taking module 110 and thedetermining unit 140.

The picture-taking module 110 keeps capturing a driving image with afocal length while the vehicle 20 is moving. Each time when thepicture-taking module 110 captures a driving image, the image analyzingunit 120 performs image recognition on the currently-captured drivingimage to search the driving image for a license-plate picture. Thedetermining unit 140 detects the picture size of the found license-platepicture according to a size threshold. If the picture size of thelicense-plate picture found is smaller than the size threshold, thedetermining unit 140 causes the adjusting unit 130 to adjust the focallength of the picture-taking module 110. To adjust the focal length, theadjusting unit 130 receives the speed of the vehicle 20 and increasesthe focal length of the picture-taking module 110 according to the speedof the vehicle 20.

To clearly describe related components, the words “first,” “second” and“third” used below are intended to distinguish the components ratherthan sort or define their differences, but the present invention is notlimited thereto.

Referring to FIGS. 1-3, at the first point in time, the picture-takingmodule 110 captures a driving image (hereinafter referred to as thefirst driving image) with a focal length of a first assigned value (stepS310). The picture-taking module 110 captures an image in focus around afirst picture-taking range R1 to obtain the first driving image.

The image analyzing unit 120 performs image recognition on the firstdriving image to search the first driving image for the license-platepicture (step S320). The determining unit 140 detects the picture sizeof the license-plate picture according to a size threshold (step S330)to determine whether the picture size of the license-plate picture issmaller than the size threshold (step S332).

If the picture size of the license-plate picture is smaller than thesize threshold, the determining unit 140 causes the adjusting unit 130to increase the focal length from the first assigned value to a secondassigned value according to the speed of the vehicle 20 (step S340).Afterward, at the second point in time, the picture-taking module 110keeps capturing a driving image (hereinafter referred to as the seconddriving image) with the focal length of the second assigned value (stepS350). At this point in time, the picture-taking module 110 captures animage in focus around a second picture-taking range R2 to obtain thesecond driving image.

When the picture size of the license-plate picture is larger than orequal to the size threshold, the adjusting unit 130 does not change thefocal length of the picture-taking module 110 such that thepicture-taking module 110 keeps capturing a driving image with the focallength of the first assigned value (that is, going back to step S310).

In some embodiments of step S340, the adjusting unit 130 generates thesecond assigned value according to an input value which is a function ofthe speed of the vehicle 20, assigns the focal length of thepicture-taking module 110 with the second assigned value thus generated,and causes the picture-taking module 110 to keep capturing a drivingimage with a focal length of the second assigned value.

In an embodiment, the vehicle camera device 10 comprises a storing unit150. The storing unit 150 is connected to the image analyzing unit 120.

Referring to FIGS. 1-4, when the picture size of the license-platepicture is larger than or equal to the size threshold, the determiningunit 140 causes the image analyzing unit 120 to perform text recognitionon the license-plate picture found in the first driving image so as toidentify a license plate number (step S360) and store the identifiedlicense plate number in the storing unit 150 (step S370).

In an embodiment, the vehicle camera device 10 comprises a displayingunit 160. The displaying unit 160 is connected to the image analyzingunit 120. After the license plate number has been identified (stepS360), the displaying unit 160 displays the current first driving imageand the license plate number related to the first driving imagesimultaneously (step S380). In some embodiments of step S380, the imageanalyzing unit 120 composites a composite image by combining the licenseplate number and the first driving image, and then the displaying unit160 displays the composite image which comprises the first driving imageand the license plate number.

Referring to FIGS. 1-3 and 5, in some embodiments, after step S350, theimage analyzing unit 120 performs image recognition on the seconddriving image to search the second driving image for a license-platepicture (step S322). After the license-plate picture has been found inthe second driving image (step S322), the image analyzing unit 120performs text recognition on the license-plate picture found in thesecond driving image, so as to identify a license plate number (stepS362) and store the license plate number in the storing unit 150 (stepS372).

In an embodiment, after the license plate number has been identified(step S362), the displaying unit 160 displays the current second drivingimage and the license plate number related to the second driving imagesimultaneously (step S382). In some embodiments of step S382, the imageanalyzing unit 120 composites a composite image by combining the licenseplate number and the second driving image, and then the displaying unit160 displays the composite image which comprises the second drivingimage and the license plate number.

Referring to FIGS. 1-3 and 6, in an embodiment, after step S350, theimage analyzing unit 120 performs image recognition on the seconddriving image to search the second driving image for the license-platepicture (step S322). The determining unit 140 detects the picture sizeof the found license-plate picture according to a size threshold (stepS334) and determines whether the picture size of the license-platepicture is smaller than the size threshold (step S336). If thelicense-plate picture is smaller than the size threshold, thedetermining unit 140 causes the adjusting unit 130 to increase the focallength from the second assigned value to a third assigned valueaccording to the speed of the vehicle 20 (step S342). Afterward, at thethird point in time, the picture-taking module 110 keeps capturing adriving image with a focal length of the third assigned value (stepS352). At this point in time, the picture-taking module 110 captures animage in focus around a third picture-taking range R3 to obtain adriving image.

Therefore, in this embodiment, the vehicle camera device 10 captures adriving image consecutively and repeatedly (step S310, S350 or S352),searches the driving image for a license-plate picture (step S320 orS322), detects the picture size of the license-plate picture accordingto the size threshold (step S330 or S332), increases the focal length ofthe picture-taking module 110 according to the speed of the vehicle whenthe picture size is smaller than the size threshold (step S340 or S342),and performs text recognition on the current license-plate picture untilthe picture size is not smaller than the size threshold or the focallength of the picture-taking module is maximized so as to identify alicense plate number (step S360). In other words, the vehicle cameradevice 10 will perform text recognition if the second assigned value isequivalent to the preceding first assigned value, or the third assignedvalue is equivalent to the preceding second assigned value.

In some embodiments, the focal length is changed by optical zoom ordigital zoom. In some embodiments, the first assigned value, secondassigned value and third assigned value are each an optical zoommultiple, such as 1×, 1.5×, 2×, 2.5×, 3×, 3.5× or a larger multiple. Thefirst assigned value is not larger than the second assigned value,whereas the second assigned value is not larger than the third assignedvalue.

In some embodiments, the size threshold is assigned and stored in thestoring unit 150 in advance. The size threshold includes a widththreshold and a height threshold. If the width of the picture size ofthe license-plate picture is smaller than the width threshold or theheight of the picture size of the license-plate picture is smaller thanthe height threshold, the determining unit 140 determines that thelicense-plate picture is smaller than the size threshold. The widththreshold is 100 pixels, 150 pixels, or 200 pixels. The height thresholdis 50 pixels, 75 pixels, or 100 pixels.

In another embodiment, in an embodiment of the present invention, thevehicle camera device 10 adjusts the focal length directly in accordancewith the speed of the vehicle 20.

Referring to FIGS. 1, 2 and 7, the adjusting unit 130 receives the speedof the vehicle 20 (step S410) and assigns an input value which is afunction of the speed of the vehicle to the focal length of thepicture-taking module 110 (step S420). Afterward, the picture-takingmodule 110 captures a driving image with the assigned focal length (stepS430). The image analyzing unit 120 performs image recognition on thedriving image to search the driving image for a license-plate picture(step S440) and recognizes the found license-plate picture so as toidentify a license plate number displayed in the license-plate picture(step S450).

In some embodiments, the image analyzing unit 120 stores the drivingimage and the license plate number related to the driving image in thestoring unit 150 (step S460).

In some embodiments, after the license plate number has been identified(step S450), the displaying unit 160 simultaneously displays the currentdriving image and the license plate number related to the currentdriving image (step S470). In some embodiments of step S470, the imageanalyzing unit 120 composites a composite image by combining the licenseplate number and the driving image, and then the displaying unit 160displays the composite image which comprises the driving image and thelicense plate number.

Referring to FIG. 8, in some embodiments, the determining unit 140receives the speed of the vehicle 20 (step S510) and detects a change inthe speed of the vehicle 20 according to a speed threshold (step S520).If the change in the speed of the vehicle 20 leads to a speed largerthan the speed threshold, the determining unit 140 enables the adjustingunit 130 to adjust the focal length of the picture-taking module 110(that is, go back to step S410). If the change in the speed of thevehicle 20 leads to a speed not larger than the speed threshold, theadjusting unit 130 does not adjust the focal length of thepicture-taking module 110. In some embodiments, the speed threshold isassigned and stored in the storing unit 150 in advance.

It should be noted that although the steps are described sequentially,the sequence is not restrictive of the present invention. Personsskilled in the art understand that under a reasonable condition somesteps can be executed simultaneously or in reverse order.

In some embodiments, the recognition technology applied in step S360 orstep S362 or step S450 is well known among persons skilled in the artand thus is not described herein for the sake of brevity.

In some embodiments, the image analyzing unit 120, the adjusting unit130 and the determining unit 140 are implemented by one or moreprocessing components. The processing components are microprocessors,microcontrollers, digital signal processors, microcomputers or centralprocessing units. The storing unit 150 is implemented by one or morestorage elements. The storage elements are exemplified by memory orregisters, but the present invention is not limited thereto.

In conclusion, a method for recognizing a license plate with a vehiclecamera device and the vehicle camera device according to the presentinvention are adapted for use with a vehicle. The focal length of thevehicle camera device is adjusted in response to the speed of thevehicle to increase the recognition rate of a license-plate picturefound in a driving image captured with the vehicle camera device.

What is claimed is:
 1. A method for recognizing a license plate, themethod comprising the steps of: capturing a first driving image by apicture-taking module of a vehicle camera device with a focal length ofa first assigned value, wherein the vehicle camera device is mounted ona vehicle; performing image recognition on the first driving image tosearch the first driving image for a license-plate picture; detecting apicture size of the license-plate picture according to a size threshold;increasing the focal length from the first assigned value to a secondassigned value according to a speed of said vehicle on which the vehiclecamera device is mounted when the picture size of the license-platepicture is smaller than the size threshold; and capturing a seconddriving image by the picture-taking module with the focal length of thesecond assigned value.
 2. The method of claim 1, further comprising thesteps of: performing image recognition on the second driving image tosearch the second driving image for the license-plate picture;performing text recognition on the license-plate picture found in thesecond driving image so as to identify a license plate number; andstoring the license plate number.
 3. The method of claim 1, furthercomprising the step of performing text recognition on the license-platepicture found in the first driving image so as to identify a licenseplate number and record the license plate number when the picture sizeof the license-plate picture is larger than or equal to the sizethreshold.
 4. The method of claim 1, wherein the first assigned valueand the second assigned value are each an optical zoom multiple.
 5. Avehicle camera device, adapted to be mounted disposed on a vehicle, thevehicle camera device comprising: a picture-taking module for capturinga driving image with a focal length; an image analyzing unit forperforming image recognition on the driving image to search the drivingimage for a license-plate picture; an adjusting unit for receiving aspeed of said vehicle on which the vehicle camera device is mounted; anda determining unit for detecting a picture size of the license-platepicture according to a size threshold and causing the adjusting unit toincrease the focal length of the picture-taking module according to thespeed of said vehicle on which the vehicle camera device is mounted whenthe picture size of the license-plate picture is smaller than the sizethreshold.
 6. The vehicle camera device of claim 5, wherein thedetermining unit causes the image analyzing unit to perform textrecognition on the license-plate picture so as to identify a licenseplate number, when the picture size of the license-plate picture islarger than or equal to the size threshold.
 7. The vehicle camera deviceof claim 6, further comprising a displaying unit for simultaneouslydisplaying the current driving image and the license plate numberrelated to the driving image.
 8. The vehicle camera device of claim 6,further comprising a storing unit for storing the driving image and thelicense plate number related to the driving image.
 9. A method forrecognizing a license plate, the method comprising the steps of:receiving a speed of a vehicle on which a vehicle camera device mounted;generating an assigned value of a picture-taking module of the vehiclecamera device according to the speed of said vehicle on which thevehicle camera device is mounted; assigning a focal length of thepicture-taking module with the assigned value; capturing a driving imageby the picture-taking module with the focal length assigned; searchingthe driving image for a license-plate picture; and recognizing thelicense-plate picture found.